In U.S. patent application Ser. No. 09/474,894, entitled "WIRELESS GROUND LINK-BASED AIRCRAFT DATA COMMUNICATION SYSTEM WITH ROAMING FEATURE," filed Jun. 2, 1999, which is a continuation of parent application Ser. No. 08/557,269, filed Nov. 14, 1995, U.S. Pat. No. 6,047,165 and entitled, "WIRELESS, FREQUENCY-AGILE SPREAD SPECTRUM GROUND LINK-BASED AIRCRAFT DATA COMMUNICATION SYSTEM," the disclosures which are hereby incorporated by reference in their entireties, a ground data link system provides a wireless mechanism for transferring data files to and from aircraft while the aircraft is on the ground at ground data linked equipped airports. In the wireless ground link-based aircraft data communication system with this roaming feature, the retrievable records of the flight performance of an aircraft are downloaded using the ground data link unit. The ground data link unit includes an archival data store operative to accumulate and store flight performance data during flight of the aircraft. A spread spectrum transceiver is coupled to the archival data store and includes a transmitter that is operative after the aircraft completes its flight and lands at an airport to download the flight performance data that has been accumulated and stored by the archival data store during flight over one of a plurality of sub-band frequency channels of a spread spectrum communication system.
An airport based spread spectrum transceiver includes a receiver that receives the spread spectrum communication signal from the aircraft and demodulates the signal to obtain the flight performance data. The airport based spread spectrum transceiver includes a probe transmission circuit that transmits a probe beacon on each sub-band frequency channel to the spread spectrum transceiver to determine which sub-band frequency channel is preferred. The probe beacon could include an interrogation signal that contains data representative of an allowable power limit of the spread spectrum communication signal that can be transmitted.
Based upon the probe beacon, the aircraft can select a particular sub-band frequency channel. However, it would be more advantageous if the aircraft ground data link unit could select a sub-band frequency channel automatically based upon a specified parameter that could be located or known, depending on the position of the aircraft.